Some banners are inexpensive items purchased for a 1 time special event, meant to be discarded after a week or two.
In other instances, they represent a significant investment that will be used over and over again. In that case, it pays to know how to care for your investment. Banners last longer when properly stored. That means rolled up, either around a cardboard core and/or rolled and put into a canvas storage case. Folding can sometimes cause creases that over time will show up when the banner is hung. Canvas storage bags are available and help keep the ropes and banner from slipping apart when storing and handling.
If the banner has been laminated with a protective clear coat, then the laminate side should always be rolled to the outside to prevent tunneling.
Consider your storage facility. It needn't be elaborate, but it shouldn't be subject to extreme temperature variations either.